Don't Tell Mum The Babysitter's Dead

When Molly and Arthur go on their first vacation since Bill was born, they hire a babysitter to take care of their kids. When the caretaker dies in her sleep, Percy is unable to get ahold of his older brothers and steps up to the plate to care for his younger siblings. How will they manage three entire months on their own? AU, based off of the movie under the same name